Diagnostic testing of wells with sustained casing pressure-An analytical approach
Document Type
Conference Proceeding
Publication Date
1-1-2018
Abstract
According to the US Minerals Management Service regulations, diagnostic testing is required in any well exhibiting sustained casing pressure (SCP). Results of the test determine if immediate SCP removal could be temporarily waived (departure permit) and continuing operation of the well permitted. The test is conducted by bleeding the casing pressure through a 0.5-inch needle valve followed by closing the valve and letting the pressure build up for 24 hours. Presently, analysis of these tests is limited because it considers only the value of pressure after a 24-hour buildup and the ability to bleed the pressure down to zero over 24-hour time period. Patterns of pressure change are not analyzed and no theory supports the analysis. The work presented here is the first attempt to develop a SCP model and understanding of casing pressure response during the testing. SCP testing data from several wells, collected and analyzed in this study, demonstrate five typical patterns of pressure response: two for pressure bleed-down and three for buildup. The variety of pressure behavior is attributed to the mechanism of gas movement in wells with SCP. The mechanism has been mathematically modeled by coupling equations for transient gas-flow through leaking cement with two-phase gas migration in mud column above the cement. The mathematical model was used to explain the five patterns of pressure response. It was found that the shape of pressure bleed-down plot is controlled only by properties of gas-cut mud above the cement top. On the other hand, the pressure buildup plot is mostly controlled by the gas flow in cement and, therefore, may provide information on the conductivity, depth and source pressure of the cement leak. Moreover, sensitivity study with the model revealed that prolonged pressure bleed-down (to avoid production of liquid) may render non-zero value of final pressure while rapid pressure release (with liquids) may temporarily bleed pressure to zero. Finally, the study showed that the 24-hour limit for pressure buildup may not be sufficiently long to determine the values of annular conductivity, depth and pressure of the gas-source formation.
Publication Source (Journal or Book title)
Canadian International Petroleum Conference 2003, CIPC 2003
Recommended Citation
Xu, R., & Wojtanowicz, A. (2018). Diagnostic testing of wells with sustained casing pressure-An analytical approach. Canadian International Petroleum Conference 2003, CIPC 2003 Retrieved from https://repository.lsu.edu/petroleum_engineering_pubs/771
